The NT1B-300TC-TSG is a specially designed version of the Teo NT1B-300TC compact ISDN Network Termination. This model has been certified by the National Telecommunications Security Working Group (NTSWG) for use in standalone applications with TSG-6 approved S/T interface ISDN terminals, such as the L-3 Communication Systems STE, or the Teo TSG-6 ISDN Phone 6220T-TSG, where the NT1 is collocated within the SCIF (Sensitive Compartmented Information Facility) area.

Complete metallic disconnection of the U interface on the ISDN Line jack is provided when the NT1 is not powered, and the design ensures that unintentional microphonic audio signals are not detectable on external wiring. Only two pins (4 and 5) are used on the U Line modular connector; all other contacts have no connection.

Teo TSG-6 products meet the requirements of the Intelligence Community Technical Specification ICD/ICS 705 for Sensitive Compartmented Information Facilities (SCIF), prepared by the National Counterintelligence Executive, which replaced DCID 6/9. Please refer to TSG-6 Guidelines.